DNA strand breaks and TDP-43 mislocation are absent in the murine hSOD1G93A model of amyotrophic lateral sclerosis in vivo and in vitro

PLoS One. 2017 Aug 23;12(8):e0183684. doi: 10.1371/journal.pone.0183684. eCollection 2017.

Abstract

Mutations in the human Cu/Zn superoxide dismutase type-1 (hSOD1) gene are common in familial amyotrophic lateral sclerosis (fALS). The pathophysiology has been linked to, e.g., organelle dysfunction, RNA metabolism and oxidative DNA damage conferred by SOD1 malfunction. However, apart from metabolically evoked DNA oxidation, it is unclear whether severe genotoxicity including DNA single-strand breaks (SSBs) and double-strand breaks (DSBs), originates from loss of function of nuclear SOD1 enzyme. Factors that endogenously interfere with DNA integrity and repair complexes in hSOD1-mediated fALS remain similarly unexplored. In this regard, uncontrolled activation of transposable elements (TEs) might contribute to DNA disintegration and neurodegeneration. The aim of this study was to elucidate the role of the fALS-causing hSOD1G93A mutation in the generation of severe DNA damage beyond well-characterized DNA base oxidation. Therefore, DNA damage was assessed in spinal tissue of hSOD1G93A-overexpressing mice and in corresponding motor neuron-enriched cell cultures in vitro. Overexpression of the hSOD1G93A locus did not change the threshold for severe DNA damage per se. We found that levels of SSBs and DSBs were unaltered between hSOD1G93A and control conditions, as demonstrated in post-mitotic motor neurons and in astrocytes susceptible to replication-dependent DNA breakage. Analogously, parameters indicative of DNA damage response processes were not activated in vivo or in vitro. Evidence for a mutation-related elevation in TE activation was not detected, in accordance with the absence of TAR DNA binding protein 43 (TDP-43) proteinopathy in terms of cytoplasmic mislocation or nuclear loss, as nuclear TDP-43 is supposed to silence TEs physiologically. Conclusively, the superoxide dismutase function of SOD1 might not be required to preserve DNA integrity in motor neurons, at least when the function of TDP-43 is unaltered. Our data establish a foundation for further investigations addressing functional TDP-43 interaction with ALS-relevant genetic mutations.

MeSH terms

  • Amyotrophic Lateral Sclerosis / genetics*
  • Amyotrophic Lateral Sclerosis / pathology
  • Animals
  • Comet Assay
  • DNA Damage*
  • DNA Repair
  • DNA Transposable Elements
  • DNA-Binding Proteins / metabolism*
  • Disease Models, Animal*
  • In Vitro Techniques
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Motor Neurons / physiology
  • Mutation
  • Real-Time Polymerase Chain Reaction
  • Spinal Cord / metabolism
  • Spinal Cord / pathology
  • Superoxide Dismutase-1 / genetics*

Substances

  • DNA Transposable Elements
  • DNA-Binding Proteins
  • SOD1 protein, human
  • TDP-43 protein, mouse
  • Superoxide Dismutase-1

Grants and funding

This work was supported by the Ministry for Economics, Sciences and Digital Society of Thuringia (TMWWDG), in the framework of the ProExcellence Initiative RegenerAging (RegenerAging-FSU-I-03/14 to AK), and by the Interdisciplinary Center for Clinical Research (IZKF) Jena (Project FF01 to AK). JG received funding from a BMBF (the Bundesministerium für Bildung und Forschung) grant in the framework of the E-RARE program (PYRAMID), JPND (OnWebDUALS and SOPHIA) of the European Union and the German Association for Neuromuscular Diseases (DGM e.V.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.